This invention relates to transfers having a discontinuous or non-uniform layer of adhesive.
The use of pressure sensitive adhesives in the production of transfers, decalcomanias, and self adhesive films requires a range of qualities in the formulation of the adhesives in which the compromises required for the ease of application and the durability of the applied product cannot both be met satisfactorily.
For transfers, decalcomanias, and self adhesive products which do not require to withstand harsh use over extended periods, the use of low tack adhesives which have just sufficient tack to adhere to the receptor surface are common.
In transfer technology, the use of low tack adhesives which are rendered less cohesive by the inclusion of tack modifying agents such as waxes, and inorganic extenders such as chalk, talc or silicas enable a multitude of indicia to be printed on the same sheet and individually transferred without accidentally transferring unselected indicia. Such adhesives can be made to adhere well to the temporary carrier sheet such that no transfer of the adhesive occurs outside the area of the indicia, the adhesive can be printed outside the area of the indicia so that accurate registration of the adhesive with complex and small indicia, for example, is not required, the adhesive shears easily around the indicia which can be transferred in close proximity to one another, say in making up the characters in a word without disturbing previously applied indicia.
However, the manipulation of the formulation of such adhesive renders the adhesive unsatisfactory for many other uses which require stronger adhesion to the receptor surface, or greater resistance to disturbance of the transfer, decalcamania, or self adhesive material once applied in industrial application, or where exterior weathering resistance is required.
Once such higher specification of the adhesive is required, it becomes unacceptable to use waxes or extenders in the same high concentrations and adhesives have to be formulated to give higher cohesion and higher tack.
When such higher performance adhesives are employed, it is difficult to control the release of one indicium from a carrier sheet and its selective transfer to a receptor surface. This is because the high tack and initial grab of the adhesive results in a large area of adhesive sticking readily to the receptor. Consequently, large parts of the transfer become attached to the receptor and individual indicium cannot be easily transferred without creasing or tearing of the designs. Other difficulties include formation of air bells due to adhesive sticking without allowing egress of air between the receptor surface and the transfer.
It is a further problem when the printed indicia are extremely thick that when the adhesive is printed normally there is a high build of adhesive around the edges of the indicia, which further complicates the problem of shear and adhesive transfer around the edges of the indicia.
In order to overcome these problems, it is the object of this invention to ensure that the ease of application previously obtained by rendering the adhesive less tacky, is obtained by physical means rather than modifying the adhesives by their formulation.